Light pipes are typically cylindrical, transparent structures through which light is channeled longitudinally by total internal reflection. Total internal reflection occurs when light is transmitted at a critical angle from one medium to another medium with a lower index of refraction. At the critical angle, light is reflected back into the medium of higher refractive index instead of being refracted by the change in media and traveling through the second medium. All or some of light transmitted through a light pipe may undergo total internal reflection. Light not internally reflected is emitted from the light pipe along the length of the light pipe.
Light pipes transmit light generated by a light source. The light source is usually contained in a lamp assembly to which the light pipe is fastened. A typical lamp assembly includes a housing that contains a light source such as a light emitting diode (LED), necessary electrical components to supply power to the light source, and a means for fastening the light pipe to the lamp assembly.
In many light pipe applications the space to accommodate the light pipe and associated lamp assembly is limited. Interior automobile lighting is an example of such an application. It is also desirable to maximize the light pipe output. Efforts to maximize output are typically directed to minimizing light degradation along the length of the pipe.
Some light pipes provide relatively even light distribution along the length of the light pipe, the projection angle of the light emitted from the light pipe is somewhat limited. In some applications, it is necessary to provide a wider distribution of the light emanating from the light pipe. In current applications, the angle of light projection may be increased by widening the reflective strip but a comparatively large increase in strip width is necessary to cause a significant difference in the projection angle. However, a large increase in the width of the reflective strip results in excessive light degradation along the length of the light pipe. Consequently, there is a need for a light pipe that provides a wide angle of light emitted from the light pipe and minimizes degradation of the illumination along the length of the pipe.
Along with increased light emissions from a light pipe via a wider angle of light emitting from the light pipe, some applications require additional characteristics of the light emitting from the light pipe. One particular need is for a light pipe that provides softer edges of the light emitting from a light pipe. In this application, the light emitted from the light pipe would not show a visibly distinct angle where the light is projecting from the light pipe. This may be required for specific “mood” lighting.